(a) Field of the Invention
The present invention relates to a torque control method for a hybrid vehicle and a system thereof. More particularly, the present invention relates to a torque control method for a hybrid vehicle and a system thereof which may provide simplified method of torque control for motor/generators and an engine.
(b) Description of the Related Art
An environmentally-friendly vehicle (i.e., a green car) typically produces relatively low pollution compared to an internal combustion engine vehicle and thus is capable of realizing a relatively high efficiency. Environmentally-friendly vehicles include hybrid vehicles, plug-in hybrid vehicles, clean diesel vehicles, fuel cell vehicles, electric vehicles and so on.
In particular, a hybrid vehicle (i.e., a hybrid electric vehicle) is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles to provide a more fuel efficient alternative to a single power source vehicle.
The hybrid vehicles may be controlled to produce maximum efficiency of an engine and motor/generators, and may regenerate energy during braking and deceleration of a vehicle by converting kinetic energy to electrical energy and thus enhance fuel consumption efficiency compared to especially conventional internal combustion engine vehicles. Also, hybrid vehicles may, at certain times, be driven without operating an engine especially in a city or congested area so that exhaust emissions may be reduced.
Hybrid vehicles generally include a BMS (Battery Management System) which manages a battery's output, predicts charging and detects the current voltage to maintain optimal battery conditions. Hybrid vehicles also typically include an ECU (engine control unit) which drives an engine and controls output of the engine by controlling an ETC (electric throttle controller) for controlling air intake, a MCU (Motor Control Unit) which outputs torque commands for a motor/generator and controls charging of the battery, a TCU (Torque Control Unit) which controls shift modes and regeneration, and a HCU (Hybrid Control Unit) which communicates with the control units and controls the overall operations of the all of the control units.
Meanwhile, during torque control for a hybrid vehicle, constraints or limitations of an engine and a motor/generator for operating at an optimal driving are variable. For example, constraints of a battery power may be variable according to changes in a SOC (state of charge), battery temperature, battery voltage and so on. Constraints of an engine torque may be variable according to changes of atmospheric temperature, atmospheric pressure or engine malfunction and so on. Constraints of a motor/generator torque may be variable according to changes of motor/generator temperature, inverter input voltage, or motor/generator malfunction and so on. Constraints of engine and motor/generator speed may be variable according to malfunctions of an engine or a motor/generator and so on.
In the conventional torque control method for a hybrid vehicle, optimal correction or compensation is accounted for individually according to various constraint changes of an engine and a motor/generator and as a result the control method becomes very complicated. Additionally, each optimal map data for each condition is input into the system, and as a result, the memory of controller must be increased excessively and still optimal correction or compensation may not be achieved according to constraint changes. Also, management of a battery is conducted separately and thus management of the battery may not be executed simultaneously.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.